SOLVED Cobalt Drive problems…..SOLVED……..FINALLY!

Jeff C

Jeff C

Active member
New member here and also new to building pedals, as you will shortly see. I previously built a BYOC Reverb pedal kit successfully and it sounds great. I’ve also built from scratch a Strat, a Tele, a 59 LP, and an LP Junior. So, I wanted a blues driver pedal and thought I’d take a whack at the Cobalt Drive from PedalPCB. The directions are not as detailed as in a kit so I’ve had some difficulty. Clearly in over my head. I managed to procure the parts from the list (not without trial and error on my part) from Tayda. I mistakenly bought a switch without solder lugs so after consulting a patient, helpful friend, bought a daughter board and did my best to figure out how to marry the two - having no skills whatsoever in electronics. History major. I have managed to assemble it but I get nothing from it except static pops when I plug it in. Bypass doesn’t work. No idea what I’ve done wrong but I suspect it revolves around needing to do more with the daughter board on the switch. But what do I know? Here’s a couple of pics (the power jack is not there but I did connect it to test). And I haven’t installed the LED yet. Any and all suggestions are eagerly welcomed. You may recomemd I should just start over but I hope not….. Thank you!
855EE297-D464-47F8-880D-F0D8B9C40E15.jpeg 15E06C0D-93DB-4AE9-944D-BA1BED3416FB.jpeg
 
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giovanni said:
Sorry I meant R6. Do you have continuity there?
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Well, I USED to at some point. But right now, I get r4 to q1 drain and r2 to q1 gate……….. Part of my frustration is that at any given moment I can get different readings. At one time, I even got audio from the IC……..Aaarrggghh.
 
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Jeff C said:
Well, I USED to at some point. But right now, I get r4 to q1 drain and r2 to q1 gate……….. Part of my frustration is that at any given moment I can get different readings. At one time, I even got audio from the IC……..Aaarrggghh.
Click to expand...
That probably means you have an intermittent short somewhere. The question is where? This kind of stuff is the trickiest. Anyways, if you don’t have continuity between R6 and the source of Q1, I’m not surprised you don’t get signal at the drain. You could try bridging R6 to the source using an alligator clip and see if you do get signal that way. I’m focusing on Q1 because it’s the very first stage and if that doesn’t work, we are SOL.
 
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For trying to find shorts open circuits etc

With no power to the circuit check resistance along whatever trace using the schematic e.g. to check Q1 source place one probe on the source pin and one on ground where you should expect R6 value 4K7 or thereabouts the resistance between Q1 source and ground

If you get infinite resistance for example ie high resistance that would indicate an open circuit/ short etc

You'd basically look along the path you suspect may have a problem and check the resistance on that node

Another example would be VREF as your reference point to Q1 gate where you'd expect R2 value 220K

Obviously it can get more complex using this method if you have paralell resistances etc to consider

You might not always get exact resistance but it should be fairly close

Just remember not to power the circuit

I'd double check D100 isn't the problem obviously if you've zilch on the cathode you've no power into the circuit

I would bypass D100 by sticking a jumper wire either side of it you could tack solder your jumper to the underside solder joints or on the diode pins
 
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I rigged up a bypass for the protective diode. Not soldered. Just wouldn’t stick to the diode pin, but I get connectivity between the two sides of the diode. Going to check power levels tomorrow……..
 
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Jeff C said:
I rigged up a bypass for the protective diode. Not soldered. Just wouldn’t stick to the diode pin, but I get connectivity between the two sides of the diode. Going to check power levels tomorrow……..
Click to expand...
It you get signal on the drain of Q1 it means your power section is fine. If it ain’t broken…
 
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